Peak-Height Distribution of Equatorial Ionospheric Plasma Bubbles: Analysis and Modeling of C/NOFS Satellite Observations

We present the first observational determination of statistical limits on the rise of equatorial plasma bubbles as a function of solar flux. We analyzed in situ electron density data collected onboard the Communications/Navigations Outage Forecasting System (C/NOFS) satellite to characterize the distribution of peak altitudes of equatorial ionospheric plasma bubbles. We first describe our algorithm for detecting ionospheric irregularities within the observations and then use a series of statistical simulations to identify and compensate for the sampling biases inherent in observations from a single satellite in a low-inclination elliptical orbit. The simulations also confirmed that space-based orbital platforms such as the C/NOFS satellite undersample the existing irregularities in the ionosphere and provide a measure of the satellite's inefficiency in observing those naturally occurring irregularities. In deducing the variation of the peak-height distributions of the irregularities with solar activity, we find that the median maximum height of the bubbles increases linearly from about 490 km at the solar minimum (2008) to 740 km during the (2014) solar maximum in the longitude sector 80 degrees W-10 degrees E. The results will be valuable for the development of improved scintillation mapping models for both real-time and postprocessing applications. We also confirm our observational findings with modeling results from a physics-based model, allowing us to identify field-line-integrated Pedersen conductance as the key determinant of terminal bubble altitude: a bubble will cease to rise further when the conductance inside the bubble is equal to that of the background ionosphere.